Compressor bleed control



, June 3, 1958 /NVENTOR BRUCE N TORELL A T TURA/E y ent of the remaining or high pressure stages.

Unite States Patent O 2,837,269 COMPRESSOR BLEED CoNTRoL Application May 3, 1954, seran No. 427,303

6 Claims. (ci. 23o-114) This invention relates to a bleed control particularly for la multi-stage aXial-ow compressor.

Bleed controls which function to prevent stalling or surging in a multi-stage compressor are well known. One feature of the present invention is the gradual closing of bleed in a multi-stage compressor so as to maintain a selected ratio between the pressure difference across the portion of the compressor from the inlet to the bleed and the pressure diierence across a similar portion of the compressor from the inlet to a stage upstream of the bleed. Another feature is the biasing of one of the pressure signals as a function of the movement of the bleed valve thereby, to make the opening or closing of the valve a gradual operation.

One feature of the invention is the application of thisl bleed system to a split compressor in which a-number of the low pressure stages operate as a unit with the rotor operating at a selected speed and the remaining or high pressure stages operating as a unit but with the rotating portions of the stages operating at a speed independently of the pressure stages;

Other W'objects and advantages will be apparent from theV specification and claims, and from the accompanying drawing which illustrates embodiments of the invention.

Fig. l is a diagrammatical view of the bleed cont-rol.

Fig. 2 is a diagrammatical view similar to Fig. 1 showing a modication. l i

The invention is shown in connection with a multistage axial-flow compressor in which a number of low pressure stages operate as a unit and at a speed independ- As shown, the compressor includes a casing 2 having a number of rows of stator vanes 4 alternating with rotating blades 6,

the latter being carried by a rotor 8 constituting the low pressure rotor. The casing also carries another series of p g ICC bleeding is` controlled by the area of the ports 28Athat is uncovered.

The piston valve 24 is moved in a directionto close the ports 28 by iluid under pressure, which in the arrangement shown, is supplied from thehigh pressure end of the compressor. In the arrangement shown,'the compressor outlet has a port 32 connectedby a conduit 34 to an inlet port 36 in a control valve casing 38. The casing has a bore40 which receives a valve plunger 42. AXially spaced from port 36 is a vent port 44 and midway between these ports is an 4outlet port 46 connected by a conduit48 to the cylinder 22 above the piston valve.

Plunger 42 has a land 50, Which, in the mid position'of the plunger shown, covers the port 46. Movement of the plunger 42 to the left, Fig. l, permits uid under pressure from port 36 to enter port 46 and from this port reach the cylinder 22 to move valve 24 to the closed position. Alternately, movement of the plunger 42 to the right vents the cylinder through port 44 to cause the bleed valve to open. p

Plunger 42 is moved in response to pressu-re changes within the compressor. As shown, this plunger has piston enlargements 52 and 54 at opposite ends, the piston 52 being larger than the other piston, as shown. These pistons are positioned in cylinders 56 and 58 forming a part of the casing 38. The inner ends of cylinders 56 and 58 are in communication by means of a passage 60 in the casing and a conduit 62 extends trom the passage to a static pressure tap 64 located in the casing 2 at theinlet to the compresso-r. The outer end of cylinder 56 is connected by a conduit 66 to a pressure tap 68 located in the compressor casing at a point between the compressor inlet and the point where the bleeding of the compressor takes place. That is to say, at a point downstream of the inlet and upstream of the bleed.

The outer end of the cylinder 58 is connected by a conduit 70 to a pressure tap 72 at Ior closely adjacent to the bleed ports 20 in the casing. With this arrangement, the plunger 42 is moved in response to changes in the ratio of low pressure compressor discharge pressure (Pf3) y minus compressor inlet pressure (Ptz) divided by the rows of high pressure stator vanes 10 alternating with rows of blades 12 carried by the high pressure rotor 14. Each of the rotors 8 and 14 is separately rotated from a split multi-stage turbine. Y

For thepurpose of improving theA part-load operation ofthe compressor and to facilitate starting, a bleed is provided between the endsof the compressor, this bleed being located in the arrangement shown between the high and low pressure portions of the compressor. To provide for this bleeding, the casing 2 ha-s a surrounding ring 16 defining an annular chamber 18 which communicates with one or more radially extending passages 20 in the casing. These passages provide communication between the chamber 16 and the air path through the cornpressor. On the outside ofthe ring is mounted a radially extending cylinder 22.having a piston valve 24 movable therein and urgedby a spring 26 in a direction to uncover ports 28jin the wall ofthe cylinder 22. The cylinder beneath the valve 24 communicates with the chamber 18 through ports* 30 so that as the ports 28 are uncovered, bleeding ofthe compressor takes place/and the amount of intermediate stage pressure (P1) minus compressorinlet.

pressure.

By suitably biasing the pressure signal from the low` pressure compressor discharge so that movement of the bleed valve 24 toward its open position tends to raise the low pressure compressor discharge pressure signal above its true value, opening or closing of the bleed valve is made a gradual operation which is some function of engine speed. To accomplish this, the conduit has a restriction 7,3 therein and downstream ofthe restriction a branch conduit 74 communicates with a chamber 76 in a casing 78 forming a projection on the cylinder 22. The outlet of the chamber 76 is a passage 80 communicating by a branch conduit 82 with the conduit 34. The casing 78l has' aneedle valve 84 therein whichy engages with the end ofthe passage 80, thereby controlling the rate of ilow out of the chamber 76. The needle valve 84 is connected to a lever arm 86 which is pivoted on a pin 88 to the casing 78 and Vconnected to its other end to a rod 90 projecting from the piston valve 24. As the bleed valve Patented June 3, :8v

3 a higher value than lthe actual pressure at the discharge of the low pressure portion of the compressor. Since the needle valve 84 is closed as the bleed valve is closed, the point of complete bleed valve closure occurs at a specific ratio of Pi-Pf2 which ratio closely aproximates a specific value of Pf3/Pta.

The arrangement shown in Fig. 2 is quite similar to Fig. 1. In this gure the bleed valve 24 is actuated by air under pressure from the compressor outlet through the conduit 34 as controlled by the Valve plunger 42. The conduit 62 connects the pressure tap at the compressor inlet to the passage 60 and the conduit 66 delivers air from an intermediate pressure tap in the compressor to -the cylinder 56 at the left hand end of the control valve. The conduit 66 has a restriction 92 therein, for a purpose that will hereinafter appear. The conduit 70 connects the cylinder 58 at the right hand end of the control valve to the pressure tap 7?. at or adjacent to the point where bleeding occurs.

In the arrangement of Fig. 2, instead of using the needle valve S4 for increasing the pressure acting on the right hand end of the contro-l valve, the needle valve in Fig. 2 functions to reduce the pressure acting on the left hand end ot' the control valve. To accomplish this, conduit 94 extends from the conduit 66' downstream of the restriction 92 to the chamber 76 in the casing 78. The passage S is connected by a branch conduit 96 to the conduit 62. Thus, as the bleed valve 24 moves into open position, the needle valve 84 also opens and increases the rate of flow from the conduit 66' into the conduit 62', thereby reducing the pressure on the left hand side of the piston 52 and increasing the pressure on the right hand side of this same piston. That is to say, the pressure signal from the intermediate low pressure compressor stage is suitably biased so that movement of the bleed valve toward open position tends to lower this pressure signal below its true value. Opening and closing of the bleed valve is thus made a gradual operation with complete closure occurring at 'a fixed low pressure compressor ratio (Pf3/Pfg).

It will be understood that the low pressure compressor pressure ratio at which bleed closure begins can be adjusted through proper contouring of the needle valve and by proper choice .of the fixed orifices of the biasing circuits.

It is to be understood that the invention is not limited to the specific embodiments herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

l. A bleed control forv a multi-stage compressor having means for bleeding air therefrom at an intermediate stage, said control including a lluid actuated closure for regulating the area of said bleed means, valve means for regulating the effect of fluid on said closure, means for actuating said valve means in one sense in response to fluid pressureadjacent to the point in the compressor where bleeding occurs, means for actuating said valve means in an opposite sense in response to iluid pressure at a point in the compressor upstream of said tirst point and means for `actuating said valve means in both senses in response to fluid pressure at the compressor inlet.

2. A bleed control for a multi-stage compressor having means for bleeding Aair therefrom at an intermediate stage, said control including a fluid actuated closure for regulating the area of said bleed means, valve means for regulating the effect of fluid on said'closure, means for actuating said valve means in one direction in response to the fluid pressure rise in the compressor between the inlet and the bleed point and means for actuating said valve means in the opposite direction in response to the tluid pressure rise in the compressor be- 4 Y tween the inlet and an intermeidate point between the inlet and the bleed point.

3..A bleed control for a multi-stage compressor having means for bleeding air therefrom, said control including a iluid actuated closure for regulating the area of said bleed means, valve means for regulating the eifect of iluid on said closure, means for actuating said valve means in one sense in response to fluid pressure adjacent to the point in the compressor where bleeding occurs,-

means for actuating said Valve in an opposite sense in response to fiuid pressure at a point in the compressor upstream of said first point, means for actuating said valve means in both senses in response to lluid pressure at the compressorinlet and means for biasing the actuation of said valve means by one of said uid pressures in accordance with the position of said closure.

4. A bleed control for a multi-stage compressor having` means for bleeding air therefrom, said control including a iluid actuated closure for regulating the area of said bleed means, a valve for regulating the effect of fluid on said closure, means for actuating said valve in one direction in response to fluid pressure from an intermediate point between the compressor inlet and the point where bleeding occurs, means for actuating said valve in the opposite direction in response to fluid pressure from the compressor adjacent to the point where bleeding occurs, valve means connected to and movable with said closure, and conduit means in which said valve means is located for biasing the actuation of said'valve means by said iluid pressure adjacent to the point where bleeding occurs in accordance with the position of said closure.

5. A bleed control for a multi-stage compressor having a plurality of low pressure stages independent of the remaining `high pressure stages such that the rotor speed for the low pressure stages isindependent of the high pressure rotor speed, said bleed control including bleed means for bleeding air between the low and high pressure stages, a fluid actuated closure for regulating the area of said bleed means, a valve for regulating the effect of fluid on said closure, means for actuating said valve in one direction in response to fluid pressure from an intermediate point between the compressor inlet and the point where bleeding occurs, means for actuating said valve in the opposite direction in response to fluid pressure from the downstream end of the low pressure compresser stages and means operatively connected with said closure for biasing the actuation of said valve means by one of said iluid pressures in accordance with the position of said closure.

- 6. A bleed control for a multi-stage compressor having a plurality of low pressure stages independent of the remaining high pressure stages such that the rotor speed for the low pressure stages is independent of the high pressure rotor speed, said bleed control including bleed means for bleeding air between the low and high pressure stages, a lluid actuated closure for regulating-the area of said bleed means, valve means for regulating the effect of iluid on `said closure, means for actuating said valve means in one direction in `response to the lluid pressure rise in the low pressure compressor stages and means for actuating said valve means in the opposite direction in response to the lluid pressure rise in the low pressure compressor between the inlet and an intermediate point between the inlet and the downstream end of the low pressure compressor stages.

References Cited in the ille of this patent i. UNITED STATES PATENTS 

